Oxygen in silicon: A positron annihilation investigation

Positron lifetime and Doppler broadening investigations of oxygen in silicon (Cz silicon) have been performed. It was found that positrons may be trapped by defects yielding a positron lifetime of only 100 ps and a momentum distribution of the annihilation quanta which is wider than that for defect-free silicon. This unequivocally shows that clusters of oxygen constitute positron traps. The trapping process was found to be thermally activated in the 25–300 K range. Isochronal and isothermal annealing showed that the clusters alternate during growth between having an interstitial character and a vacancy character. At 450 and 500 °C, growth of oxygen clusters takes place with an activation energy of 1.5 eV, while at 650 and 714 °C, these clusters disappear with an activation energy of 1.1 eV. At 714 and 790 °C, growth of new clusters takes place with an activation energy of 2.6 eV.